Digital broadcast receiving system for detecting short-breaks and holding information based on same

ABSTRACT

A receiver is constructed so that it detects a short-break of a digital broadcasting wave by the absence of a synchronizing code or by a transmission control signal multiplexed with the broadcasting wave and, according to the short-break detection signal, holds data and state information (program arrangement, and reference time information) obtained by an antenna and converter ( 1 ), tuner and digital decoding portion ( 2 ), an error correction code decoding portion ( 3 ), a stream multiplexed signal separating portion ( 4 ), an audio/video decoding portion ( 5 ) and the other components and performs a process for optimally changing characteristics of closed loops for establishing synchronization.

TECHNICAL FIELD TO WHICH THE INVENTION PERTAINS

The present invention relates to a digital broadcast receiver forreceiving a digital broadcasting program via a broadcasting satellite(BS) and, more specifically, to the receiver provided with a controlsystem capable of adaptively controlling the broadcast reception when ashort break of a RF-signal occurs due to changing a transmitting stationto another at the receiver or due to discontinuity of signal by changinga transmitting system at the transmission station.

BACKGROUND OF THE INVENTION

A short break of a RF-signal can be noticed in advance by using atransmission control signal multiplexed with a digital broadcastingsignal via a BS. However, there has been no idea of adaptive control ofthe receiver to smoothly restoring the broadcast reception against aimmediately ceasing short break (wave discontinuity) of a broadcastingsignal, which may occur without the notice when a transmission system ischanged to another at a broadcast transmitting station. A receiverprovided with means for realizing the above-mentioned idea has not yetproposed.

In other words, no proposal has been made in regard to a receivercontrolling method that, when a broadcast signal is instantaneouslybroken (with discontinuity) and immediately restores itself to normalstate, can adaptively control the reception of the broadcast byre-synchronizing and presenting video-and-audio signals. A broadcastingwave may suffer attenuation by the effect of some local surroundingconditions such as a heavy rainfall, resulting in decreasing thesignal-to-noise ratio of the signal. The short break of a broadcastingsignal may take place when, to improve the C/N ratio in such asituation, a viewer at a receiver changes a current receivedtransmitting station to another or an operator at a transmitting stationchanges a current transmitter to another.

There has not yet been proposed a receiver that has means fordiscriminating whether a signal is instantaneously broken (it may berestored to normal state after a very short period) or broken (no signalis transmitted for a long time for some reason) and control meansadapted to realizing prompt pull-in for re-synchronization and smoothreturning presentation of normal video-audio signals after ceasing ofthe short break.

Once a signal was broken, a conventional receiver, taking noconsideration of whether signal can be restored with a short break,detects the out-of-synchronization, stops presentation of an image,mutes the sound output, searches a tunable frequency, retunes andrestarts reception of data (e.g., service information in the MPEG2 andthe so on). In other words, the receiver performs substantially the sameprocess as it must perform after turning on its power supply.

If it is previously known that the signal will be instantaneously brokenand immediately restored to the normal state, the receiver desirablymaintains acquired data and state until the broken signal is restored toits normal state. This enables the receiver to promptly restart normalvideo/audio presentation, i.e., to return to the normal operation.

SUMMARY OF THE INVENTION

Accordingly, a receiver that can detect an instantaneously restorableshort-break or discontinuity of a broadcasting signal and perform aspecially designated process enabling a viewer to look and listen thevideo-audio presentation without sensing the actual short-break(discontinuity) of a signal.

In practice with a short-break of a signal, the receiver detects it,keeps in its memory acquired data and receiving conditions until acontinuous signal is restored and, then, optimally controls thereturning process to promptly restart the normal audio-videopresentation. Namely, the present invention has as its primary objectthe provision of a receiver that can promptly restore the presentationof normally restored signal with a possibly shortest break(discontinuity) that cannot be sensed by the viewer. This receiver canthus solve the problem of the prior art receiver that has to perform aprolonged restart process substantially corresponding to its startprocess beginning at turning on its power supply.

The receiver detects a break or discontinuity of a received signal anddiscriminates whether it prolongs or whether it is a short break by atransmission control signal multiplexed with a digital broadcastingwave. According to the discrimination result, the receiver holds tuningdata such as a center frequency of a tuner and a frequency offset andcontrols closed-loop transmission functions of carrier and clock (clocksignal) of a phase shift keying (PSK) demodulating portion to obtain awider pull-in range and a shorter lock-up time. It holds information onan error of phase shift between an internal counter and a program clockreference (PCR) of a digital phase locked loop (PLL), stops updating ofinformation by decoding a video image and presents an immediatelypreceding image signal. Furthermore, the receiver stops detecting andupdating of a presentation time stamp (PTS) and the PCR, changes ajitter range for PCR according to received C/N and controls itself so asto promptly transit to normal operation after a short-break.

The receiver can thus operate to minimize the disordered audio-visualpresentation to the viewer due to the discontinuity of the signal duringthe returning process.

The present invention is provided with the following technical means:

(1) Accordingly, an object of the present invention is to provide adigital broadcast receiving system for receiving a transport streamtransmitted according to the MPEG standard and presenting decodedbroadcast information comprising: a synchronization detecting means fordetecting a synchronizing code in the transport stream; a short-breakdiscriminating means for discriminating whether a transport streamsuffers a short-break or not according to synchronizing-code lackingduration determined from the synchronizing-code detection made by thesynchronization detecting means; and a returning process control meansfor performing a process of returning to normal operation after ceasinga short-break of the broadcasting wave by controlling at least one of:means for holding tuning information of a tuner; means for controllingclosed-loop transmission functions of carrier and clock of demodulatingportion; means for holding phase error information of a digitalphase-locked loop (PLL) according to a program clock reference (PCR);means for stopping updating the decoded image presentation andpresenting an immediately preceding image signal; means for stoppingdetecting/updating a presentation time stamp (PTS); and means forstopping detecting/updating the PCR and changing a jitter range for thePCR, wherein the normal operation of the receiving system after ceasinga short-break of the transport stream is restored by driving thereturning process control means according to a result of discriminationmade by the short-break discriminating means.

(2) Another object of the present invention is to provide a digitalbroadcast receiving system for receiving a digital broadcasting wave andpresenting demodulated broadcasting information comprising: atransmission control signal detecting means for detecting a transmissioncontrol code multiplexed with the digital broadcasting wave; a framesynchronization detecting means for detecting a frame synchronizingsignal in the digital broadcasting wave; a short-break discriminatingmeans for determining whether the broadcasting wave suffers ashort-break or not according to synchronization lacking durationdetermined from a result of detection made by the short-breakdiscriminating means; a short-break pre-announcing means for givingnotice of a short-break of a digital broadcasting wave by a content ofthe transmission control signal detected by the transmission controlsignal detecting means; and a returning process control means forperforming a process for returning to normal operation after ceasing ashort-break of the digital broadcasting wave by controlling at least oneof: means for holding tuning information of a tuner; means forcontrolling closed-loop transmission functions of carrier and clock of aphase-shift keying (PSK) demodulator; means for holding a phase errorinformation of a digital phase-locked loop (PLL) according to a programclock reference (PCR); means for stopping updating the decoded imagepresentation and presenting an immediately preceding image signal; meansfor stopping detecting/updating a presentation time stamp (PTS); andmeans for stopping detecting/updating the PCR and changing a jitterrange for the PCR, wherein the normal operation of the receiving systemafter ceasing a short-break of the broadcasting wave is restored bydriving the returning process control means according to a result ofdiscrimination made by the short-break discriminating means or a resultof the notice made by the short-break pre-announcing means.

(3) A further object of the present invention is to provide a digitalbroadcast receiving system for receiving a digital broadcasting wave andpresenting demodulated broadcasting information comprising: atransmission control signal detecting means for detecting a transmissioncontrol signal multiplexed with the digital broadcasting wave; a closedloop detecting means for detecting a pull-in state of closed loop of aclock or a carrier of a phase-shift keying demodulator; a short-breakdiscriminating means for discriminating whether the broadcasting wavesuffers a short-break or not according to a closed-loop's pull-in stateand duration detected by the closed loop detecting means; a short-breakpre-announcing means for giving notice of a short-break of a digitalbroadcasting wave by a content of the transmission control signaldetected by the transmission control signal detecting means; and areturning process control means for performing a process of returning tonormal operation after ceasing a short-break of the digital broadcastingwave by controlling at least one of: means for holding tuninginformation of a tuner; means for controlling closed-loop transmissionfunctions of carrier and clock of a phase-shift keying (PSK)demodulator; means for holding phase error information of a digitalphase-locked loop (PLL) according to a program clock reference (PCR);means for stopping updating the decoded image presentation andpresenting an immediately preceding image signal; means for stoppingdetecting/updating a presentation time stamp (PTS); and means forstopping detecting/updating the PCR and changing a jitter range for thePCR, wherein the normal operation of the receiving system after ceasinga short-break of the broadcasting wave is restored by driving thereturning process control means according to a result of discriminationmade by the short-break discriminating means or a result of the noticemade by the short-break pre-announcing means.

(4) A still further object of the present invention is to provide adigital broadcast receiving system for receiving a digital broadcastingwave and presenting demodulated broadcasting information comprising: atransmission control signal detecting means for detecting a transmissioncontrol signal multiplexed with the digital broadcasting wave; ashort-break discriminating means for determining whether thebroadcasting wave suffers a short-break or not according to logic of thetransmission control signal detected by the transmission control signaldetecting means; and a returning process control means for performing aprocess of returning to normal operation after ceasing a short-break ofthe broadcasting wave by controlling at least one of: means for holdingtuning information of a tuner in specified time after the short-break;means for controlling closed-loop transmission functions of carrier andclock of a phase-shift keying (PSK) demodulator; means for holding phaseerror information of a digital phase-locked loop (PLL) according to aprogram clock reference (PCR); means for stopping updating the decodedimage presentation and presenting an immediately preceding image signal;means for stopping detecting/updating a presentation time stamp (PTS);and means for stopping detecting/updating the PCR and changing a jitterrange for the PCR, wherein the normal operation of the receiving systemafter ceasing a short-break of the broadcasting wave is restored bydriving the returning process control means according to a result ofdiscrimination made by the short-break discriminating means.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic block diagram of a digital broadcasting satellite(BS) receiver according to the present invention.

FIG. 2 is a block diagram of a signal short-break detecting systemaccording to an embodiment of the present invention.

FIG. 3 is a block circuit diagram of a part of a tuning and digitaldecoding portion, which performs operations necessary for tuning to areceive frequency.

FIG. 4 is a block circuit diagram of a part of a tuning and digitaldecoding portion, which circuit performs operations for acquiring acarrier and correcting a clock.

FIG. 5 is a block diagram of a circuit for performing operation forfreezing in an image-decoding portion.

FIG. 6 is a block diagram of a circuit for generating a reference systemclock of a program clock reference (PCR).

FIG. 7 is block diagram of a circuit for performing the control ofpresentation by a presentation time stamp (PTS).

FIG. 8 is a block diagram of a short-break detection circuit of anembodiment of the present invention.

DESCRIPTION OF PREFERRED EMBODIMENTS OF THE PRESENT INVENTION

A digital broadcast receiver according to a preferred embodiment of thepresent invention will be described bellow with reference to theaccompanying drawings.

FIG. 1 illustrates a schematic construction of a digital broadcastreceiver embodying the present invention.

Digital compressed audio-visual signals of multiplexed pluralbroadcasting programs are modulated in phase, upconverted in frequencyand then transmitted via a broadcasting satellite to digital broadcastreceivers.

The transmitted radio-frequency (RF) signals are received by a digitalbroadcast receiver through an antenna converter 1 and down-converted toa first intermediate frequency (IF) signal to be input tuning anddigital decoding portion 2 of the receiver installed indoor.

At this time, the converter must transform polarization plane of thereceived wave since the wave from a communication satellite is anorthogonally polarized wave and the wave from a broadcasting satelliteis a circularly polarized wave. The tuner must select suitable one ofdifferent first intermediate frequencies according to the frequency bandarrangement of the received wave.

The tuning and digital demodulating portion 2 tunes the receiver to thereceive frequency according to the received signal wave and demodulatesthe phase-modulated digital signals. For example, the broadcasting viathe communication satellite is demodulated according to the QPSKmodulation, while the broadcasting via the broadcasting satellite isdemodulated according to the 8PSK modulation.

A tuning center frequency of a synthesizer-tuner is externally set to apreviously known receive frequency.

The digital demodulating portion (demodulator) is usually provided witha closed loop for locking a received slippage of frequency or a carrierwave and a closed loop for locking a digital-conversion clock at anoptimal phase. It has functions for optimizing the demodulation.

The demodulated signal is input to an error correction code decodingportion 3 that in turn decodes a stream encoded by a suitable codingmethod according to propagation characteristics of differenttransmission paths (e.g., satellite, earth, cable and so on). The errorcorrection code decoding portion for the communication satelliteincludes Viterbi decoding, convolutional de-interleaving, transmissionde-scrambling, Reed-Solomon decoding and MPEG synchronization code(frame) detection. A main function of this portion is to detect andresolve a sync code (synchronization code) encoded by the errorcorrection coding method and highly protected against a transmissionerror that may occur specifically on each transmission path.

The error correction code decoding portion for the broadcastingsatellite includes Viterbi decoding or Trellis decoding, separation anddecoding of a transmission control code, block de-interleaving,transmission descramble, Reed-Solomon decoding and transmission framesynchronization code detection.

The decoded stream having a structure clearly defined after capturing asynchronization code, correcting a transmission path error and decodingtransmission path codes is input to a stream multiplexed signalseparating portion 4. The input stream contains a large number ofmultiplexed program arrangement information, time stamps and compressedvideo-audio signals.

The stream multiplexed signal demultiplexing portion 4 has functions forreading various kinds of multiplexed program-related information (e.g.,IDs) from the program-arrangement information, generating a decodingsystem clock from the time stamps, managing the presentation time andselectively separating a desired program.

A compressed video-audio data stream of a selectively separated programis supplied to an audio/video decoding portion 5. The compressivelycoded data is based on the MPEG method. The audio/video decoding portion5 expands the compressed information and outputs decoded data to apresentation device 6 that in turn presents audio-visual presentation.

This is a summary of a structure of the digital broadcast receiver andits operation.

The operation of a receiver according to an aspect of the presentinvention will be described in detail with reference to the relateddrawings.

FIG. 2 is a block diagram of a short-break detecting portion fordetecting a short break of a received signal. The portion shown in FIG.2 is included in the transmission path code decoding portion of theembodiment shown in FIG. 1.

The circuit of FIG. 2 receives an input of demodulated digital signaltuned to the received frequency corresponding to the received signalwave. A sync code detecting portion 30 separates specified sync codes(47hex) from the decoded signal, defines them as synchronizing-codes byits periodicity (one for every 188 bytes) and detects a sync position (abeginning point of the stream). The sync signal is supplied to async-acquisition discriminating portion 31.

The sync-acquisition discriminating portion 31 determines forwardprotection length and backward protection length and discriminateswhether the synchronism is acquired or not by using the above protectionlengths. The backward protection discrimination is such that asynchronizing position is determined whereat n sync-signals are detectedin succession. The forward protection discrimination is such that thesynchronism cannot be acquired (established) if m sync signals arelacking in succession.

A unit time measuring portion 32 considers a short (instantaneous) breakof a signal is defined if the time for which the synchronism cannot beacquired is less than a specified threshold. A prolonged break isdefined if the above time is equal or grater than the above threshold.Namely, the receiver is designed to perform a special process for ashort break less than the threshold and return to a usual restartprocess if the out-of-sync period exceeds the threshold.

The special process to be performed with a short break thusdiscriminated will be described in detail bellow.

FIG. 3 is a detailed illustration of a part of the tuning and digitaldecoding portion of FIG. 1.

As shown in FIG. 3, a radio frequency (RF) signal down-converted to afirst stage intermediate frequency (IF) is input to a tuning portion 20.In case of demodulating the input signal by using, e.g., a QPSKquasi-synchronous method, a center tuning frequency is set externally,and the input signal is multiplied by a phase-shifted output and anon-phase-shifted output, respectively, of a fixed oscillator to producedetection signals of orthogonal axes IQ.

Then, the signals from the tuning portion 20 are sampled for example ata frequency twice the symbol rate by an A/D converter and demodulated bya digital demodulating portion 21. In the digital demodulating portion21, a difference between a tuning frequency and a desired receivingfrequency (slippage of frequency and polarity) is detected. Thepreviously set center frequency is corrected by adding thereto thefrequency difference (error) by an adder 12, thus the tuning frequencyis optimally corrected.

In the usual operation, once the acquisition of synchronism becameunable, receivable frequencies are searched from the previously receivedprogram arrangement information with reference to a table of satellitefrequencies and possible causes of the out-of-sync state is examined. Inthis case, the frequency error data is discarded and, in general,reset-and-restart process is begun.

In the embodiment of the present invention, a frequency error, whichcorresponds to a slippage between a synchronizing frequency and adesired frequency, is kept for a specified short-break period and usedfor tuning the a restored signal, shortening the necessary tuning time.

FIG. 4 is a detailed illustration of a part of a tuning anddigital-decoding portion shown in FIG. 1, which part is intended tocapture a carrier and correct a clock.

In FIG. 4, a tuning portion 20 outputs a detection signal of tunedorthogonal axes IQ. This detection signal is converted by the A/Dconverter into digital signal to be input to a digital demodulatingportion 21.

The digital demodulating portion 21 includes a clock closed loop 21K forcontrolling a sampling clock frequency and a phase for digitalconversion and a carrier closed loop 21C for capturing a carrier.

The carrier closed loop 21C is composed of a complex multiplier, aroll-off filter, a frequency phase error detector, a loop filter, anumerically controlled oscillator and a cosine-sine converter.

A carrier wave is input to the complex multiplier wherein phase errordata of the carrier frequency is determined by referring to an errorconversion table matching a real part, an imaginary part of the carrierwave and its modulation method. The numerically controlled oscillator isthen controlled through the loop filter of the secondary closed loop.The oscillator output is converted by the cosine-sine converter into asine wave signal that is then applied to the complex multiplier todetect again the phase error data of the carrier wave.

A transmission function of each closed loop is changed so that a pull-intime may be optimally shortened when a short-break occurs. Once thecarrier was captured, the transmission function is further changed to besuitable to hold the carrier. This enables the receiver to quicklycapture the carrier and reliably hold it.

In practice, this control system optimally selects anattenuation-constant and the secondary loop 21 k, i.e., a ratio ofcoefficients of a proportional part and an integrating part of thetransmission function 21K.

Furthermore, the transmission function of the clock loop is similarlychanged to have an optimally shortened pull-in time when a short-breakoccurs. Once the phase was locked, the transmission function is furtherchanged to be suitable to hold the locked phase. This enables thereceiver to quickly lock the loop and reliably hold the locked phase.

The clock loop 21K forms a closed loop that can detect a phase errorfrom data at a zero-crossing sampling point in the digital demodulatingportion 21 and normalize the zero-crossing sampling point to be of zero.

FIG. 5 is a block diagram of a circuit for freezing a presentationsignal in an image decoder of the audio/video decoding portion 5.

According to FIG. 5, the operation of the circuit is as follows:

When a short break was detected, a random access memory (RAM) forstoring data used for a short-break duration is supplied repeatedly withthe same image data already stored therein without updating withnewly-decoded image, thus realizing continuous presentation of thenormal preceding image.

This example is to hold the presentation of a preceding image in placeof a shortly broken signal. Alternatively, an image may be muted. Mutingan audio signal may be a best countermeasure.

FIG. 6 is a block diagram of a circuit for generating a reference systemclock and time-markers for program clock reference (PCR). This circuitis included in the error correction path code decoding portion of thereceiver according to the embodiment of FIG. 1.

As shown in FIG. 6, a transport stream MPEG is input to a terminal of aPCR detecting portion 33. Respective data units are developed accordingto the header information and flags in the stream. The PCR data servingas a basis of system synchronization is extracted as an output data ofthe PCR.

The initially extracted PCR data is set on an internal counter 34 (SCR)that starts counting of the same data value. A deference (error) betweena value currently extracted by the PCR detecting portion 33 and a countvalue of the internal counter 34 is input through a digital loop filterto a D-A converter by which it is converted into an analog value. Thecorresponding voltage is applied as an oscillator control voltage to avoltage controlled crystal oscillator (VCXO) that generates a clock(clock signal) that is used as a reference clock to be counted by theinternal counter 34. A closed loop is thus formed.

When a short-break discriminating signal is input to a common terminal,the PCR detecting portion 33 stops redetection of the PCR and theinternal counter 34 stops counting.

To prevent erroneous detection of PCR by the PCR detecting portion 34and erroneous count by the internal counter 34 due to the effect of ashort break of a signal, the error value just before the short break isheld for causing the oscillator to generate a fixed value. When a normalsignal is restored, the above-mentioned initial process is restarted,thereby the closed loop stably restart the operation, realizing theimmediate pull-in state.

FIG. 7 is a block diagram of a circuit for performing the control ofpresentation according to a presentation time stamp (PTS). The circuitshown in FIG. 7 is included in the audio/video decoding portion of thereceiver according to the embodiment shown in FIG. 1.

Presentation-related information (e.g., the PTS indicating a relativepresentation time multiplexed with image information) is separated andextracted by a PTS detecting and lag/lead detecting portion 35.

A lag/lead is detected by determining a difference from an internalreference time (offsetting is possible) of the internal counter (SCR)and the presentation time is adjusted by a delay 36. With a short breakof a signal, the image information is not newly decoded since a newinput stream is not correct and the internal counter (SCR) stopscounting. Detection of a new PTS is continued but data is not updated.The delay therefore becomes constant. Consequently, presentation of ajust preceding image can be stably repeated.

The receiver having the above structure can smoothly restore its normaland stable operation.

Alternative method for detecting a short-break of an input signal inanother embodiment of the present invention will be described below.(The practical control with a short break is similar to that of thepreceding embodiment.)

FIG. 8 is a block diagram of a short-break detection circuit accordingto an embodiment of the present invention. The circuit shown in FIG. 8is contained in the transmission-line-code decoding portion of theembodiment of FIG. 1.

As shown in FIG. 8, digital data demodulated by a digital demodulatingportion is input to a frame sync detecting portion 37.

For example, a frame synchronizing signal multiplexed with data to betransmitted by a broadcasting satellite is a known fixed code that isinserted at specified intervals. The specificity and periodicity of thesynchronizing code is used for detection of the frame synchronization.

The frame synchronization (sync) detecting portion 37 determines forwardprotection length and backward protection length, discriminates whetherthe synchronism is acquired on one side and the synchronization is notacquired on the other side if the conditions are satisfied. For example,the backward protection determines the acquisition of thesynchronization (synchronized position) if n pieces of sync signals aredetected in succession while the forward protection determines theimpossibility of acquiring the synchronization if m pieces of syncsignals lack in succession.

The synchronizing signal from the synchronization detecting portion 37is input to the synchronization acquisition and short-breakdiscriminating portion 38, by which a break of a received signal isdiscriminated as a short break if the time of inability to acquire thesynchronization did not exceed a specified threshold period and it isdiscriminated as a prolonged break if inability to acquire thesynchronization exceeded a specified threshold period.

Namely, the portion determines the occurrence of a short-break beingshorter than the threshold period and causes the system to carry out thespecial process for that period or determines the occurrence of theprolonged break over the threshold period and begins the usual restartprocess. Furthermore, a gate generating portion 39G generates a gatesignal to be used for extracting a transmission control signal from thereference frame synchronizing signal multiplexed with the broadcastingwave. The transmission control signal separating portion 39 separatesthe transmission signal by using the above gate signal.

The extracted transmission control signal decoding portion conductserror correction and decoding of the transmission control signalaccording to the transmission system and then extracts a short-breaknotifying code. This notice code is a signal used, for example, as anadvance notice of site diversity. In this instance, this signal canpreviously notify a short break of several microseconds.

The notifying signal is input to the sync acquisition and short breakdiscriminating portion (unit time Measurement) 38 that decides theoccurrence of a short break by a signal from the unit time counter orthe notifying signal. In this instance, it is also possible to speed upthe detection of the sync signal acquisition by setting a backwardprotection length of frame sync detection portion 37 shorter than ausual value just after detecting a short-break.

Another short-break detection technique according to another embodimentof the present invention will be described below.

This technique is to discriminate a short break of the broadcasting waveby using the above described notifying code or a discrimination signalobtained by comparing an error signal of a digital demodulating portion21 of FIG. 4 with a preset threshold value.

In the latter case, detection process is to detect whether an errorsignal of a carrier loop or an error signal of a clock loop exceeds acertain threshold or not, binarizes the result to form a logical signaland then measure logical signals formed for a unit duration. A shortbreak is discriminated based on the count result.

In case of a short break of the broadcasting wave, the receiver may usesa special processing including changing a jitter range of PCR and SCR,which is one of means for optimal control of the entire system.

Usually, when the jitters exceeds the jitter range, the processing isperformed to decrease jitter within the jitter range by repeating orskipping a B-frame. If the jitter falls within the range, an internaldelay is used to match two data units with each other.

If a short break is detected by occasional lacking of a PCR in spite ofits continuity (SCR and PCR being the same) before and after the shortbreak, it is possible to quickly restore a non-jitter state by settingthe jitter range narrower than usual range and changing the range for aframe skipping or repeating unit.

For the receiver, storing previously obtained program arrangementinformation and a viewer's history is an essential condition forcarrying out the above-described operation.

Another short-break detection technique according to another embodimentof the present invention will be described below.

The short break may be discriminated by referring to informationtransmitted from the transmission station, which information indicates achange of an up-linking station (advance notice of site diversity)included in a transmission control signal multiplexed with a digitalsatellite broadcasting wave.

Having detected a short-break notice included in the transmissioncontrol signal, the receiver begins the holding process against theshort break that will arise after the elapse of a certain time.

In practice, as shown in FIG. 8, the receiver separates a transmissioncontrol signal by a transmission-control signal separating portion 39,decodes the above short break information by a transmission controlsignal decoding portion 39D and discriminates whether the break isinstantaneous or not. If so, the receiver starts the adaptive control ofthe broadcasting wave reception after a certain time elapsed.

As described above, when the discontinuity of a signal is detected by areceiver and a stream having close continuation to the stream before ashort break is restored with an elapse of very short time, it isdesirable for the receiver to hold the almost data obtained and keep thecontinuity of its state before and after the short break.

INDUSTRIAL APPLICABILITY

As described above, the present invention enables a receiver to operatethe continuity of its operation in the event of a short break of areceived signal and therefore to quickly restore the audio-visualpresentation, i.e., restore its normal working state in restarting thereceived signal. When an instantaneous break (the discontinuity) of asignal stream is irrevocably caused by switching a transmitter toanother at a transmission station, a user can continuously view thepresentation without sensing its discontinuity at the receiver. In otherwords, the receiver can minimize the affection of instantaneous break ofthe broadcasting transmission service.

The present invention can provide a receiver for receiving a transportstream according to MPEG standards, which can effectively discriminate ashort break based on a time for which a sync code (synchronizing code)is missing in the transport stream.

The present invention can also provide a receiver for receiving adigital broadcasting wave (including a transmission control signalmultiplexed therewith), which can effectively discriminate a short breakbased on a time for which a frame sync signal is missing or a previousnotice of a short break, which notice is contained in a transmissioncontrol signal.

The present invention can further provide a receiver for receiving adigital broadcasting wave (including a transmission control signalmultiplexed therewith), which can effectively discriminate a short breakaccording to a pull-in state and a pull-in time of closed loop of acarrier or a clock of a PSK demodulating portion or a previous notice ofa short-break, which notice is contained in a transmission controlsignal.

The present invention can still further provide a receiver for receivinga digital broadcasting wave (including a transmission control signalmultiplexed therewith), which can effectively discriminate a short breakaccording to a logic of a transmission control signal.

What is claimed is:
 1. A digital broadcast receiving system forreceiving a transport stream transmitted according to the MPEG standardand presenting decoded broadcast information comprising: asynchronization detecting means for detecting a synchronizing-code inthe transport stream; a short-break discriminating means for determiningwhether a transport stream suffers a short-break or a prolonged breakaccording to synchronizing-code lacking duration determined from thesynchronizing-code detection made by the synchronization detectingmeans, so that when a time that adequate reception of the synchronizingcode exceeds a predetermined threshold it is determined that thetransport stream suffers the prolonged break, but when a time thatadequate reception of the synchronizing code does not exceed thepredetermined threshold it is determined that the transport streamsuffers the short break; and a returning process control means forperforming a restart process when a prolonged break is determined, butperforming a process of returning to normal operation after ceasing of adetermined short-break of a broadcasting wave by controlling at leastone of: means for holding tuning information of a tuner; means forcontrolling closed-loop transmission functions of carrier and clock ofdemodulating portion; means for holding phase error information of adigital phase-locked loop (PLL) according to a program clock reference(PCR); means for stopping updating a decoded image presentation andpresenting an immediately preceding image signal; means for stoppingdetecting/updating a presentation time stamp (PTS); and means forstopping detecting/updating the PCR and changing a jitter range for thePCR, wherein the normal operation of the receiving system after ceasinga short-break of the transport stream is restored by driving thereturning process control means according to a result of discriminationmade by the short-break discriminating means.
 2. A digital broadcastreceiving system for receiving a digital broadcasting wave andpresenting demodulated broadcasting information comprising: atransmission control signal detecting means for detecting a transmissioncontrol code multiplexed with the digital broadcasting wave; a framesynchronization detecting means for detecting a frame synchronizingsignal in the digital broadcasting wave; a short-break discriminatingmeans for determining whether the broadcasting wave suffers ashort-break or not according to synchronization lacking durationdetermined from a result of detection made by the short-breakdiscriminating means; a short-break pre-announcing means for givingnotice of a short-break of a digital broadcasting wave by a content ofthe transmission control signal detected by the transmission controlsignal detecting means; and a returning process control means forperforming a process for returning to normal operation after ceasing ashort-break of the digital broadcasting wave by controlling at least oneof: means for holding tuning information of a tuner; means forcontrolling closed-loop transmission functions of carrier and clock of aphase-shift keying (PSK) demodulator; means for holding a phase errorinformation of a digital phase-locked loop (PLL) according to a programclock reference (PCR); means for stopping updating a decoded imagepresentation and presenting an immediately preceding image signal; meansfor stopping detecting/updating a presentation time stamp (PTS); andmeans for stopping detecting/updating the PCR and changing a jitterrange for the PCR, wherein the normal operation of the receiving systemafter ceasing a short-break of the broadcasting wave is restored bydriving the returning process control means according to a result ofdiscrimination made by the short-break discriminating means or a resultof the notice made by the short-break pre-announcing means.
 3. A digitalbroadcast receiving system for receiving a digital broadcasting wave andpresenting demodulated broadcasting information comprising: atransmission control signal detecting means for detecting a transmissioncontrol signal multiplexed with the digital broadcasting wave; a closedloop detecting means for detecting a pull-in state of closed loop of aclock or a carrier of a phase-shift keying demodulator; a short-breakdiscriminating means for discriminating whether the broadcasting wavesuffers a short-break or not according to a closed-loop's pull-in stateand duration detected by the closed loop detecting means; a short-breakpre-announcing means for giving notice of a short-break of a digitalbroadcasting wave by a content of the transmission control signaldetected by the transmission control signal detecting means; and areturning process control means for performing a process of returning tonormal operation after ceasing a short-break of the digital broadcastingwave by controlling at least one of: means for holding tuninginformation of a tuner; means for controlling closed-loop transmissionfunctions of carrier and clock of a phase-shift keying (PSK)demodulator; means for holding phase error information of a digitalphase-locked loop (PLL) according to a program clock reference (PCR);means for stopping updating a decoded image presentation and presentingan immediately preceding image signal; means for stoppingdetecting/updating a presentation time stamp (PTS); and means forstopping detecting/updating the PCR and changing a jitter range for thePCR, wherein the normal operation of the receiving system after ceasinga short-break of the broadcasting wave is restored by driving thereturning process control means according to a result of discriminationmade by the short-break discriminating means or a result of the noticemade by the short-break pre-announcing means.
 4. A digital broadcastreceiving system for receiving a digital broadcasting wave andpresenting demodulated broadcasting information comprising: atransmission control signal detecting means for detecting a transmissioncontrol signal multiplexed with the digital broadcasting wave; ashort-break discriminating means for determining whether thebroadcasting wave suffers a short-break or a prolonged break accordingto logic of the transmission control signal detected by the transmissioncontrol signal detecting means; and a returning process control meansfor performing a first process in response to a determined prolongedbreak, and performing a different second process of returning to normaloperation after ceasing of a determined short-break of the broadcastingwave by controlling at least one of: means for holding tuninginformation of a tuner in specified time after the short-break; meansfor controlling closed-loop transmission functions of carrier and clockof a phase-shift keying (PSK) demodulator; means for holding phase errorinformation of a digital phase-locked loop (PLL) according to a programclock reference (PCR); means for stopping updating a decoded imagepresentation and presenting an immediately preceding image signal; meansfor stopping detecting/updating a presentation time stamp (PTS); andmeans for stopping detecting/updating the PCR and changing a jitterrange for the PCR, wherein the normal operation of the receiving systemafter ceasing a short-break of the broadcasting wave is restored bydriving the returning process control means according to a result ofdiscrimination made by the short-break discriminating means.
 5. Adigital broadcast receiving method for receiving a transport streamtransmitted according to the MPEG standard and presenting decodedbroadcast information comprising: a synchronization detector fordetecting a synchronizing-code in the transport stream; a short-breakdiscriminator for discriminating whether a transport stream suffers ashort-break or a prolonged break according to synchronizing-code lackingduration determined from the synchronizing-code detection made by thesynchronization detector; and a controller(s) performing a first processin response to a determined prolonged break, and performing a differentsecond process of returning to normal operation after ceasing of adetermined short-break of a broadcasting wave by controlling at leastone of: holding tuning information of a tuner; controlling closed-looptransmission functions of carrier and clock of demodulating portion;holding phase error information of a digital phase-locked loop (PLL)according to a program clock reference (PCR); stopping updating adecoded image presentation and presenting an immediately preceding imagesignal; stopping detecting/updating a presentation time stamp (PTS); andstopping detecting/updating the PCR and changing a jitter range for thePCR, wherein the normal operation after ceasing a short-break of thetransport stream is restored by driving the a returning processcontroller according to a result of discrimination made by theshort-break discriminator.